The present invention relates to an air-fuel ratio control apparatus of an internal combustion engine.
There is known an air-fuel ratio control apparatus of an internal combustion engine in which when fuel of the internal combustion engine is increased and output of an oxygen concentration sensor provided downstream from a catalytic converter shows rich, an air-fuel ratio is controlled to a lean side during a predetermined time and then, the air-fuel ratio is returned to a theoretical air-fuel ratio (see Japanese Patent Application Laid-open (JP-A) No. 63-117139). As other arts related to the present invention, there are patent documents JP-A Nos. 63-134835, 6-307271, and 59-173533.
When CO or HC exists in exhaust gas, the exhaust gas purifying catalyst oxidizes CO or HC using occluded oxygen or oxygen in the exhaust gas. When oxide component such as NOx is included in the exhaust gas, the exhaust gas purifying catalyst reduces the oxide component using HC or CO in the exhaust gas, thereby purifying the exhaust gas. In order to meet the requirement of enhanced emission control, a capacity of catalyst of the exhaust gas purifying catalyst mounted in a vehicle or the like is increased. Therefore, in the conventional air-fuel ratio control, after fuel increasing operation of the internal combustion engine, the amount of oxygen occluded in the exhaust gas purifying catalyst until the vehicle decelerates or stops is small, and there is an adverse possibility that generation of a catalyst exhaust odor (concretely, an odor of hydrogen sulfide (H2S)) cannot be suppressed.